Leaders of the 20 richest countries will acknowledge the existential threat of climate change and will take urgent steps to limit global warming, a draft communique seen ahead of the COP26 summit shows.

As people around the world prepared to demonstrate their frustration with politicians, Pope Francis lent his voice to a chorus demanding action, not mere words, from the meeting starting on Sunday in Glasgow, Scotland.

The Group of 20, whose leaders gather on Saturday and Sunday in Rome beforehand, will...